Concrete mixing apparatus



Dec. 8, 1964 R. P. GREEN 3,160,398

CONCRETE MIXING APPARATUS Filed Jan. 24, 1965 4 Shets-Sheqt 1 1964 Y R. P. GREEN 3,160,398

CONCRETE MIXING APPARATUS Filed. Jan. 24, 1963 4 Sheets-Sheet 2 Dec. 8, 1964 R. P. GREEN 3,160,398

CONCRETE MIXING APPARATUS Filed Jan. 24, 1963 4 Sheets-Sheet I5 Dec. 8', 1964 R. P. GREEN 98 CONCRETE MIXING APPARATUS Filed'Jan. 24, 1963 4 Sheets-Sheet 4 FORWARD Mar/an Raw-23:

United States Patent 3,169,398 CQNCRETE MIXENG APPARATUS Rowland Fercy Green, Bath, gonierset, England, assignor to Stothert & Pitt, Limited, Bath, Somerset, England a corporation of the United Kingdom Filed Ian. 24, 1963, Ser. No. 253,659 7 Claims. (Cl. 259-177) This invention relates to concrete mixing apparatus and is concerned with a truck or transit mixer for the delivery of ready-mixed concrete. 7

In a truck mixer or agitator it has been the practice in the past to drive the mixing drum for the concrete by means of a power unit separate from the prime mover, by which the truck is propelled.

In handling concrete the advantages to be gained from the use of hydraulic transmission as distinct from a mechanical drive have been realized, due mainly to the fact that the hydraulic transmission is totally enclosed and therefore is not only dirtproof but is lighter and occupies a smaller space. This has led to the replacement of a separate engine and the mechanical drive by a hydraulic drive powered from the prime mover of the vehicle.

In transit to the site, it is desirable that the mixing drum should be rotated at a constant speed, usually about 2 rpm, but on the site this speed has to be increased to discharge the mix. In order to provide for an increase in speed, proposals have been made to make use of two hydraulic pumps, both of which can be coupled to the vehicle engine in order that the additional power and speed shall be available to rotate the drum as required.

According to the present invention to make use of an infinitely variable displacement hydraulic pump driven from the vehicle engine, means being provided automatically to adjust the setting or delivery of the pump so that its output remains constant on variations in engine speed.

In accordance with the invention, concrete mixing apparatus comprises the combination with a drum mixer mounted to revolve on a transporting vehicle for the delivery of ready-mixed concrete, of a prime mover for the vehicle and an hydraulic drive to the mixing drum including a variable output pump coupled to the prime mover, a motor in the output circuit from the pump for imparting drive to the mixing drum and control means whereby the output from the pump is maintained constant on variation in the speed of the prime mover.

The variable displacement pump may be mounted at the front or rear of the vehicle engine, being coupled to the prime mover through a direct or indirect drive so that diiiiculties in regard to change speed gear do not arise when in transit as they can do if the drive is taken from the gearbox.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which,

FIGURE 1 is a perspective view of one arrangement according to the invention,

FIGURE 2 is an hydraulic circuit diagram,

FIGURE 3 is a detail of a compensating device which controls a pump output,

FIGURE 4 is a plan View generally corresponding with that of FIGURE 1 but showing an alternative arrangement, and

FIGURE 5 is a diagram of an alternative hydraulic circuit for use with the arrangement shown in FIG- URE 4.

As shown in FIGURES 1 to 3 there is proyided, mounted on a chassis 1, a concrete mixing drum 2 which 3,169,398 Patented Dec. 8, 1964 "ice supplied from a variable displacement hydraulic pump 5 which is powered by the vehicle engine 6. The pump 5 can be mounted at the front of the vehicle, and can be coupled to the engine 6 through direct or indirect drive means, one of which is indicated at 7, so that diiiiculties with regard to change speed gears do not arise when in transit.

A pump output control member, as shown at rod 8, fitted integral with the pump 5, is directly coupled to a mechanical linkage compensating device 9 which controls the pump output and is provided with operating arms 10 and 11. The member 8 is settable tovary the pump output at a given pump speed in a well known manner.

Three control levers 12, 13 and 14 which may be positioned at the rear of the vehicle for the convenience of the operator, are provided. Control lever device12, by which the pump displacement can be varied to suit requirements, is coupled through a rod 15 to the arm 10 of the device 9. Control lever 13, which controls the engine throttle, is connected through a rod 16, to the accelerator gear 17 of the vehicle which gear is in turn connected through a rod 18, to the arm 11 of the device 9. The accelerator means 17 is, as usual, variis driven, through gearing 3, from an hydraulic fixed ably positionable according to the desired speed of the engine 6. Control lever 14 is connected, through a rod 15, to a valve 20 which serves to reverse the direction of oil flow to the hydraulic motor 4 in order to reverse the direction of rotation of the drum 2.

The compensating device 9 may consist of two eccentric cams disposed about a common pivot point, the throw of the cams being such that movement of arm 11 with arm 10 restrained in any one position, increases or reduces the pump displacement in such a relationship to the engine speed that output of the pump remains constant. The position of arm 10 determines the selected output.

As shown in FIGURE 2, fluid is passed from an oil reservoir 21, through a suction line 22, to the suction side of the pump 5. An infinity line 23 is also connected between the reservoir 21 and thepump 5. The output side of the pump 5 is connected, by a pressure line 24, to the direction control valve 29 whichin turn is connected, through pressure lines 25, 26 to the motor 4. A return line 27 is connected between the valve 29 and the reservoir 21. In addition the pressure lines 24, 25 and 26 are connected, through non-return valves pro vided in a manifold 28 and through lines 29, 3t) and 31, to a relief valve 32 which is connected to the reservoir by a return line 33.

In operation, the output of the pump 5 is controlled by the compensating device 9 in such. manner that, on an increase in enginethrottle opening, the pump displacement mechanism is automatically compensated in order to reduce the pump displacement and to maintain the constant pump output and thus also thespeed of rotation of the mixing drum 2 ata pre-selected speed.

In use, before transit, the engine-throttle 13 is set at idling speed and the pump delivery control lever 12 is set, when the vehicle is stationary, to give the required drum speed, usually about 2 rpm. In transit, when the accelerator pedal 17 is operated to vary the engine speed, the mechanical linkage provided by the rod 18 and the arm 11 to the device 9, is effective to transmit any movement of the accelerator pedal to the control device 9 so that the pump displacement would be varied automatically to maintain constant flow. Thus the output of the motor 4 should remain constant irrespective of engine speed.

The pump 5 in this case is of the infinitely variable displacement rotary type, of the kind described in British patent specifications Nos. 816,556 and 819,565.

In a modified arrangement, not illustrated, the relationship between the engine speed and the pump output could be effected through a separate governor, which would be connected to the arm 11 of the device 9, and not through the accelerator pedal. The governor, which may be of the centrifugal type and driven from any convenient point on the engine, such as the injector pump drive or the crank shaft, would be providedso that its working position would be directly proportional to the engine speed independent of the accelerator pedal position. This arrangement may be particularly useful since it is conceivable that, under certain conditions, Where the accelerator pedal is connected to the device 9, the particular position of the accelerator pedal and the engine speed may not always be the same on various occasions. Such a situation may arise where inefficient use is made of the gears so that the engine will tend to be overladen and will not achieve its correct governed speed for any one accelerator position.

As shown in FIGURES 4 and 5, an alternative arrangement may include, as before, an hydraulic fixed displacement motor 4 driven by a variable displacement hydraulic pump 5' which is powered by the vehicle engine 6 through a drive shaft 7. The output shaft 34 of the motor 4 is coupled, as before, through gearing 3 to the mixing drum 2.

In this embodiment the pump 5 is of the axial-piston tilting-head type, of the kind manufactured and sold by Dowty Hydraulic Units Limited under the trade name Dowmatic. In this pump the angle of the pumping elements is altered in order to adjust the stroke of the pistons and thus also the output and direction of flow of the pump. The pump is such that the angle of the pumping elements indicated at 35 can be varied by a servo unit 36 from the position indicated in full lines, where rotation of the motor 4 is in one direction, to the position indicated in broken lines, where rotation of the motor 4 is in the opposite direction, the intermediate position being a neutral position. Thus the entire flow can be reversed within the pump.

The motor 4 is in closed circuit with the pump 5' through fluid lines 37 and 38, hereinafter referred to as the main circuit. a

As in the previous arrangement, a hand controlled throttle lever 13 is connected through a rod 16 to the accelerator gear 17, which includes an accelerator pedal 39 of the engine 6.

The output of the pump 5 is controlled by a constant speed device 40, which in this case would replace the compensating device 9, and is coupled to the servo unit 36 which effects angular movement of the pumping elements 35. A hand operated control lever 41 is connected, through a linkage system 42, to the device 40 to enable the operator to vary or pre-set the output of the pump 5'. This lever is the equivalent of the lever 12 of the previous arrangement and, due to the type of pump used, eliminates the necessity of providing a separate reversing control lever.

The displacement of the pump 5' is indirectly controlled by the flow rate of a make up pump 43, variation in flow bringing about pressure difference in the unit 40 which in turn influences the servo unit 36 setting and consequently the displacement of pump 5'. This function is carried out during the agitating condition requiring automatic adjustment for constant speed. A flow controller 44 having a control lever 54 controls the op eration of the constant speed device 40 by pressure generated by the make up pump 43, in a manner described below. The flow controller 44 does not influence the automatic operation of the constant speed device 49 whilst lever 54 is in the one position. When lever 54 is in the other position the unit 40 is influenced to give a higher agitating speed. The drive shaft 45 of the pump 43 is coupled to the engine 6 by a secondary shaft 46, the shaft 7, and a belt and pulley drive 47.

This arrangement is such that both pumps 5' and 43 are driven from the engine 6 so that the speed ratio between them remains constant.

The pump 43 is of relatively small capacity as compared to the pump 5 and is mounted in a secondary circuit which consists of a suction line 48 which draws fluid from a reservoir 49 and a return line 50 which passes through a relief valve block 51 back to the reservoir 49. A filter 52, and, if required, a cooler 53 may be included in the return line 50. The pump 43 in addition to effecting adjustment of the device 40 according to the engine speed, serves to pressurise thesuction lineof the main circuit in order to reduce the possibility of cavitation in said suction line and also to make up losses due to leakage of the main pump 5.

The flow controller 44 has a control lever 54 which is capable of being placed into an operative or an inoperative position. In the inoperative position of the lever 54 the pressure in the subsidiary circuit, effected by the pump 43, is passed through pressure line 55 to the constant speed device 40 where it will be translated into a pressure difference which will in turn be transmitted to the servo unit 36. This out of balance pressure causes the movable element, of the servo unit to vary its position which in turn motivates the pump 5 to alter its displacement so as to maintain its constant output. In the operative position of the lever 54 the flow controller 44 is effective to direct pressure fluid to act through the line 56 to the control device 40 to give an alternative increased drum agitating speed which will be constant. This enables the operator to increase the drum agitating speed if required during transit, for example when operating on steep gradients in orderto reduce the likelihood of drum spillage.

In addition the circuit may also include pressure relief valves mounted in the block 51Which are connected respectively through line 57 to the servo unit 36 and through lines 58 to both sides of the motor 4; a drain line or lines 59 between the motor 4, the pump 5' and the reservoir 49; and pressure gauges 6t) and 61 which are connected respectively through line 62 to both sides of the pump 5 and through line 63 to the block 51. In addition a manual unloader lever 64 may also be provided in association with the block 51.

In use, before transit, the engine throttle lever 13 is set at idling speed whilst the vehicle is stationary and the control lever 41 is set to provide a pre-selected drum agitating speed of, for example 2 r.p.m.

In transit, any variation in engine speed will be transmitted to the pump 43. The effect of variation in flow of the pump 43 will then, as hereinbefore described, be transmitted through the constant speed device 40 and the servo unit 36 to the pump 5' in such manner as to vary the working parts thereof to maintain a constant output such as to cause the motor 4 to be driven at a speed which will drive the drum 2 at a speed of, for example, 2 rpm. If it is desired to speed up the drum agitating speed, the control lever 54 can, be moved into its operative position so that, as hereinbefore described, the constant speed control 40 will be influenced to effect greater displacement of the pump 5. I

On arrival at the site, the operator actuates the control lever 41 to reverse the direction of rotation of the drum 2 in order to discharge its contents, and thereafter the speed of rotation to effect discharge is controlled by the lever 41 in combination with the engine throttle.

It will be understood that the output of the pump 5 will be dependent both upon its displacement setting (lever 41)and the speed of the engine and that either operation can be carried out independently to achieve increase in drum speeds as a part of the maximum speed possible.

The invention provides, by ensuring that the delivery rate :fnom the hydraulic pump remains constant, the following advantages:

(1) Maintenance of a constant pre-selected mixing drum speed irrespective of vehicle engine speed to prevent overmixing.

(2) Reduction in wear and tear of the transmission and mixing drum.

(3) Minimum power taken from the vehicle engine while in transit.

(4) Improved running conditions with regard to the fluid medium and in the transmission system.

(5) Cheaper, simpler and lighter design than systems involving two pumps in order to achieve the same speed range.

(6) Vehicle control is improved during acceleration and retarding periods on the road because the drum does not alter its speed of rotation. This means that lower powered engines can be employed on the vehicle.

What is claimed is:

1. Concrete mixing apparatus comprising in combination, a drum mixer mounted to revolve on a transporter vehicle for the delivery of ready-mixed concrete; a prime mover for said vehicle; means variably positionable according to the speed of said prime mover; a hydraulic drive for said drum mixer including a variable displacement pump operatively coupled to said prime mover and having a pump output control member which is set table to vary the pump output at a given pump speed, and a hydraulic motor in the ouput circuit from said variable displacement pump for imparting drive to said mixing drum; and means operable automatically in response to positioning of said variably positionable means for setting said pump output control member to maintain the pump output constant when the speeds of said prime mover and said pump vary.

2. Concrete mixing apparatus comprising in combina- 7 drum mixer including a variable displacement pump operatively coupled to said prime mover and having a pump output control member which is settable to vary the pump output at a given pump speed, and a hydraulic motor in the output circuit from said variable displacement pump for imparting drive to said mixing drum; a control device for varying the setting of said pump output control member; and compensating means interconnecting said accelerator and said control device for modifying the setting of said pump output control member under the influence of said control device for maintaining the pump output constant when the speeds of said prime mover and said pump are varied by operation of said accelerator.

3. Concrete mixing apparatus according to claim 2 including a manually operable valve for reversing said hydraulic motor. 1

4. Concrete mixing apparatus comprising in combination, a drum mixer mounted to revolve on a transporter vehicle for the delivery of ready-mixed concrete; a variable speed prime mover for said vehicle; a hydraulic drive for said drum mixer including a variable displacement pump operatively coupled to said prime mover and having a pump output control member which is settable to vary the pump output at a given pump speed, and a hydraulic motor in the output circuit from said variable displacement pump for imparting drive to said mixing drum; and control means for automatically maintaining the Output of said pump constant when the speeds of said prime mover and said pump vary, said control means comprising a second and relatively small capacity pump coupled to said prime mover, and fluid pressure operable means connected to said pump outlet control member and being operable by fluid pressure generated by said 7 second pump for setting said pump output control member in accordance with the speeds of said prime mover and said pumps.

5. Apparatus as claimed in claim 4, including a hydraulic reservoir and a main and closed hydraulic circuit in which said variable displacement pump and said bydraulic motor are arranged, and a secondary hydraulic circuit in which said hydraulic iiuid reservoir and said second pump are arranged.

6. Apparatus as claimed in claim 5, in which said secondary circuit includes a flow controller arranged between said second pump and said fluid pressure operable means, said flow controller being adapted to effect automatically the setting of said fluid pressure operable means in order to increase the agitating speed of said drum mixer, if desired, during transit.

7. Apparatus as claimed in claim 6, in which said- References Cited by the Examiner UNITED STATES PATENTS 1/61 Feistel 259-177 3/63 Lendved 259-177 CHARLES A, WILLMUTH, Primary Examiner. 

1. CONCRETE MIXING APPARATUS COMPRISING IN COMBINA- ON TION, A DRUM MIXER MOUNTED TO REVOLVE ON A TRANSPORTER VEHICLE FOR THE DELIVERY OF READY-MIXED CONCRETE; A PRIME MOVER FOR SAID VEHICLE; MEANS VARIABLY POSITIONABLE ACCORDING TO THE SPEED OF SAID PRIME MOVER; A HYDRAULIC DRIVE FOR SAID DRUM MIXER INCLUDING A VARIABLE DISPLACEMENT PUMP OPERATIVELY COUPLED TO SAID PRIME MOVER AND HAVING A PUMP OUTPUT CONTROL MEMBER WHICH IS SETTABLE TO VARY THE PUMP OUTPUT AT A GIVEN PUMP SPEED, AND A HYDRAULIC MOTOR IN THE OUTPUT CIRCUIT FROM SAID VARIABLE DISPLACEMENT PUMP FOR IMPARTING DRIVE TO SAID MIXING DRUM; AND MEANS OPERABLE AUTOMATICALLY IN RESPONSE TO POSITIONING OF SAID VARIABLY POSITIONABLE MEANS FOR SETTING SAID PUMP OUTPUT CONTROL MEMBER TO MAINTAIN THE PUMP OUTPUT CONSTANT WHEN THE SPEEDS OF SAID PRIME MOVER AND SAID PUMP VARY. 